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Spin Study at JLab: from Longitudinal to Transverse

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J. P. Chen, Jefferson Lab Berkeley Summer Spin Program, 2009, LBNL, California Introduction Longitudinal and transverse spin Selected results from JLab – PowerPoint PPT presentation

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Title: Spin Study at JLab: from Longitudinal to Transverse


1
Spin Study at JLab from Longitudinal to
Transverse
  • J. P. Chen, Jefferson Lab
  • Berkeley Summer Spin Program, 2009, LBNL,
    California
  • Introduction
  • Longitudinal and transverse spin
  • Selected results from JLab
  • Recently completed and planned measurements
  • 12 GeV plan

2
Strong Interaction and QCD
  • Strong interaction, running coupling 1
  • -- QCD accepted theory for strong
    interaction
  • -- asymptotic freedom (2004 Nobel)
  • perturbation calculation works at
    high energy
  • -- interaction significant at intermediate
    energy
  • quark-gluon correlations
  • -- interaction strong at low energy
    (nucleon size)
  • confinement
  • theoretical tools
  • pQCD, OPE, Lattice QCD, ChPT,
  • A major challenge in fundamental physics
  • Understand QCD in strong interaction
    region
  • ? Study and understand nucleon structure

as
E
3
Nucleon Structure and Sum Rules
  • Global properties and structure
  • Mass 99 of the visible mass in
    universe
  • 1 GeV, but u/d quark mass
    only a few MeV each!
  • Momentum quarks carry 50
  • Spin ½, quarks contribution 30
    Spin Sum Rule
  • Magnetic moment large part anomalous,
    gt150 GDH Sum Rule
  • Axial charge
    Bjorken Sum Rule
  • Angular momentum
    Jis Sum Rule
  • Polarizabilities (Spin, Color)
  • Tensor charge

4
Three Decades of Spin Structure Study
  • 1980s EMC (CERN) early SLAC
  • quark contribution to proton spin is very
    small
  • DS (12-9-14) ! spin
    crisis
  • (Ellis-Jaffe sum rule violated)
  • 1990s SLAC, SMC (CERN), HERMES (DESY)
  • DS 20-30
  • the rest gluon and quark orbital angular
    momentum
  • A0 (light-cone) gauge (½)DS Lq DG
    Lg1/2 (Jaffe)
  • gauge invariant (½)DS
    Lq JG 1/2 (Ji)
  • A new decomposition (X. Chen, et. al)
  • Bjorken Sum Rule verified to lt10 level
  • 2000s COMPASS (CERN), HERMES, RHIC-Spin, JLab,
  • DS 30 DG probably small, orbital angular
    momentum probably significant
  • Transversity, Transverse-Momentum Dependent
    Distributions
  • Generalized Parton Distributions

5
Unpolarized and Polarized Structure functions

6
Parton Distributions (CTEQ6 and DSSV)
Polarized PDFs

Unpolarized PDFs
CTEQ6, JHEP 0207, 012 (2002)
DSSV, PRL101, 072001 (2008)
7
Jefferson Lab Experimental Halls
6 GeV polarized CW electron beam Pol85, 180mA
Will be upgraded to 12 GeV by 2014
HallA two HRS Hall
BCLAS Hall C HMSSOS
8
Jefferson Lab Hall A Experimental Setup for
inclusive polarized n (3He) Experiments
9
Hall A polarized 3He target
  • longitudinal,
  • transverse and vertical
  • Luminosity1036 (1/s)
  • (highest in the world)
  • High in-beam polarization
  • gt 65
  • Effective polarized
  • neutron target
  • 12 completed experiments
  • 1 are currently running
  • 6 approved with 12 GeV (A/C)

15 uA
10
Hall B/C Polarized proton/deuteron target
  • Polarized NH3/ND3 targets
  • Dynamical Nuclear Polarization
  • In-beam average polarization
  • 70-90 for p
  • 30-40 for d
  • Luminosity up to 1035 (Hall C)
  • 1034 (Hall B)

11
JLab Spin Experiments
  • Results
  • Moments Spin Sum Rules and Polarizabilities
  • Higher twists g2/d2
  • Quark-Hadron duality
  • Spin in the valence (high-x) region
  • Just completed
  • d2p (SANE) and d2n
  • Transversity (n)
  • Planned
  • g2p at low Q2
  • Future 12 GeV
  • Inclusive A1/d2,
  • Semi-Inclusive Transversity, TMDs,
    Flavor-decomposition
  • Review Sebastian, Chen, Leader, arXiv0812.3535,
    PPNP 63 (2009) 1

12
Longitudinal Spin (I)
Spin in Valence (high-x) Region
13
Valence (high-x) A1p and A1n results
Hall A E99-117, PRL 92, 012004 (2004)
PRC 70, 065207 (2004)
Hall B CLAS, Phys.Lett. B641 (2006) 11

14
pQCD with Quark Orbital Angular Momentum
F. Yuan, H. Avakian, S. Brodsky, and A. Deur,
arXiv0705.1553
Inclusive Hall A and B and Semi-Inclusive Hermes
BBS
BBSOAM
15
Projections for JLab at 11 GeV
A1p at 11 GeV
16
Flavor decomposition with SIDIS
Du and Dd at JLab 11 GeV
Polarized Sea
17
Longitudinal Spin (II)
Quark Hadron Duality in Spin Strcuture Function
18
Duality in Spin-Structure Hall A E01-012 Results
A13He (resonance vs DIS)
  • g1/g2 and A1/A2 (3He/n) in resonance region,
  • 1 lt Q2 lt 4 GeV2
  • Study quark-hadron duality in spin structure.
  • ltResonancesgt ltDISgt ?
  • PRL 101, 1825 02 (2008)

19
Duality in Spin-Structure Partial Moment Results
G1 resonance comparison with pdfs
20
Spin Sum Rules Zeroth Moments
Sum Rules
Moments of Spin Structure Functions
?
Global Property
21
Bjørken Sum Rule
gA axial vector coupling constant from
neutron b-decay CNS Q2-dependent QCD
corrections (for flavor non-singlet)
  • A fundamental relation relating an integration of
    spin structure functions to axial-vector coupling
    constant
  • Based on Operator Product Expansion within QCD or
    Current Algebra
  • Valid at large Q2 (higher-twist effects
    negligible)
  • Data are consistent with the Bjørken Sum Rule at
    5-10 level

22
Gerasimov-Drell-Hearn Sum Rule Circularly
polarized photon on longitudinally polarized
nucleon
  • A fundamental relation between the nucleon spin
    structure and its anomalous magnetic moment
  • Based on general physics principles
  • Lorentz invariance, gauge invariance ? low
    energy theorem
  • unitarity ? optical theorem
  • casuality ? unsubtracted dispersion relation
  • applied to forward Compton
    amplitude
  • First measurement on proton up to 800 MeV (Mainz)
    and up to 3 GeV (Bonn)
  • agree with GDH with assumptions for
    contributions from un-measured regions
  • New measurements from LEGS, MAMI(2),

23
Generalized GDH Sum Rule
  • Many approaches Anselmino, Ioffe, Burkert,
    Drechsel,
  • Ji and Osborne (J. Phys. G27, 127, 2001)
  • Forward Virtual-Virtual Compton Scattering
    Amplitudes S1(Q2,n), S2(Q2, n)
  • Same assumptions no-subtraction dispersion
    relation
  • optical theorem
  • (low energy
    theorem)
  • Generalized GDH Sum Rule

24
Connecting GDH with Bjorken Sum Rules
  • Q2-evolution of GDH Sum Rule provides a bridge
    linking strong QCD to pQCD
  • Bjorken and GDH sum rules are two limiting cases
  • High Q2, Operator Product Expansion
    S1(p-n) gA ? Bjorken
  • Q2 ? 0, Low Energy Theorem
    S1 k2 ? GDH
  • High Q2 (gt 1 GeV2) Operator Product Expansion
  • Intermediate Q2 region Lattice QCD calculations
  • Low Q2 region (lt 0.1 GeV2) Chiral Perturbation
    Theory
  • Calculations HBcPT Ji, Kao, Osborne,
    Spitzenberg, Vanderhaeghen
  • RBcPT Bernard, Hemmert,
    Meissner
  • Reviews Theory Drechsel, Pasquini,
    Vanderhaeghen, Phys. Rep. 378,99 (2003)
  • Experiments Chen, Deur,
    Meziani, Mod. Phy. Lett. A 20, 2745 (2005)

25
JLab E94-010 (Hall A) Neutron spin structure
moments and sum rules at Low Q2
GDH integral on neutron
  • Q2 evolution of neutron spin structure moments
  • (sum rules) with pol. 3He
  • transition from quark-gluon to hadron
  • Test cPT calculations
  • Results published in several PRL/PLBs

Q2
PRL 89 (2002) 242301
26
First Moment of g1p and g1n G1p and G1n
Test fundamental understanding
ChPT at low Q2, Twist expansion at high Q2,
Future Lattice QCD
G1p
G1n
E94-010, from 3He, PRL 92 (2004) 022301
E97-110, from 3He, preliminary EG1a, from d-p
EG1b, arXiv0802.2232 EG1a, PRL 91, 222002
(2003)
27
G1 of p-n
EG1b, PRD 78, 032001 (2008) E94-010 EG1a PRL
93 (2004) 212001
28
Effective Strong Coupling
A new attempt at low Q2
Experimental Extraction from Bjorken Sum
29
The strong coupling constant from pQCD
as (Q) is well defined in pQCD at large Q2. Can
be extracted from data (e.g. Bjorken Sum
Rule). Not well defined at low Q2, diverges
at LQCD
30
Definition of effective QCD couplings
G. Grunberg, PLB B95 70 (1980) PRD 29 2315
(1984) PRD 40 680(1989).
Prescription Define effective couplings from a
perturbative series truncated to the first term
in as.
Generalized Bjorken sum rule
Use

to define an effective
asg1. Process dependent. But can be related
through Commensurate scale relations S.J.
Brodsky H.J Lu, PRD 51 3652 (1995)? S.J.
Brodsky, G.T. Gabadadze, A.L. Kataev, H.J Lu, PLB
372 133 (1996)? Extend it to low Q2 down to 0
include all higher twists.
31
Effective Coupling Extracted from Bjorken Sum
A. Deur, V. Burkert, J. P. Chen and W. Korsch
PLB 650, 244 (2007) and PLB 665, 349 (2008)
as/p
32
Comparison with theory
?
Fisher et al. Bloch et al. Maris-Tandy Bhagwat et
al. Cornwall Godfrey-Isgur Constituant
Quark Model Furui
Nakajima Lattice
Schwinger -Dyson
Furui Nakajima
33
Transverse Spin (I) Inclusive
g2 Structure Function and Moments Burkhardt -
Cottingham Sum Rule
34
g2 twist-3, q-g correlations
  • experiments transversely polarized target
  • SLAC E155x, (p/d)
  • JLab Hall A (n), Hall C (p/d)
  • g2 leading twist related to g1 by
    Wandzura-Wilczek relation

  • g2 - g2WW a clean way to access twist-3
    contribution
  • quantify q-g correlations

35
Precision Measurement of g2n(x,Q2) Search for
Higher Twist Effects
  • Measure higher twist ? quark-gluon correlations.
  • Hall A Collaboration, K. Kramer et al., PRL 95,
    142002 (2005)

36
BC Sum Rule
0ltXlt1 Total Integral
P
Brawn SLAC E155x Red Hall C RSS Black Hall A
E94-010 Green Hall A E97-110 (preliminary) Blue
Hall A E01-012 (very preliminary)
N
BC Measlow_xElastic
Meas Measured x-range
3He
low-x refers to unmeasured low x part of the
integral. Assume Leading Twist Behaviour
Elastic From well know FFs (lt5)
37
BC Sum Rule
P
BC satisfied w/in errors for JLab Proton 2.8?
violation seen in SLAC data
N
BC satisfied w/in errors for Neutron
(But just barely in vicinity of Q21!)
3He
BC satisfied w/in errors for 3He
38
BC Sum Rule
What can BC tell us about Low-X?
P
N
Unmeasured Low-X
DIS -(RESELAS)
3He
39
Spin Polarizabilities
Higher Moments of Spin Structure Functions at Low
Q2
40
Higher Moments Generalized Spin Polarizabilities
  • generalized forward spin polarizability g0
  • generalized L-T spin polarizability dLT

41
Neutron Spin Polarizabilities
  • dLT insensitive to D resonance
  • RB ChPT calculation with resonance for g0 agree
    with data at Q20.1 GeV2
  • Significant disagreement between data and both
    ChPT calculations for dLT
  • Good agreement with MAID model predictions
  • g0
    dLT

E94-010, PRL 93 (2004) 152301
Q2

Q2

42
CLAS Proton Spin Polarizability
g0p
g0p Q6
  • EG1b, Prok et al.
  • arXiv0802.2232
  • Large discrepancies with ChPT!
  • Only longitudinal data, model for transverse
    (g2)
  • g0 sensitive to resonance

43
Summary of Comparison with cPT
  • IAn G1P
    G1n G1p-n
    g0p g0n dLTn
  • Q2 (GeV2) 0.1 0.1 0.05 0.1 0.05
    0.16 0.05 0.05 0.1 0.1
  • HBcPT poor poor good poor good good
    good bad poor bad
  • RBcPT/D good fair fair fair good
    poor fair bad good bad
  • dLT puzzle dLT not sensitive to D, one of the
    best quantities to test cPT,
  • it disagrees with neither
    calculations by several hundred !
  • A challenge to cPT theorists.
  • Very low Q2 data g1/g2 on n(3He) (E97-110)
  • g1 on p and d
    available soon (EG4)
  • Recently approved g2 on proton E08-027

44
New Experiment Proton g2 and ?LT
E08-027 A- rating by PAC33
K. Slifer, A. Camsonne, ,J. P. Chen
  • Critical input to Hydrogen Hyperfine Calculations
  • Violation of BC Sum Rule suggested at large Q2
  • State-of-Art ?PT calcs fail dramatically for ?LT

Septa Magnets for low Q2 Transverse bPolarized
Proton Target
n
?LT Spin Polarizability
BC Sum Rule
45
Color Polarizabilities
Higher Moments of Spin Structure Functions at
High Q2
46
Color Polarizability (or Lorentz Force) d2
  • 2nd moment of g2-g2WW
  • d2 twist-3 matrix element

d2 and g2-g2WW clean access of higher twist
(twist-3) effect q-g correlations Color
polarizabilities cE,cB are linear combination of
d2 and f2 Provide a benchmark test of Lattice
QCD at high Q2 Avoid issue of low-x
extrapolation Relation to Sivers and other
TMDs?
47
Measurements on neutron d2n (Hall A and SLAC)
48
d2(Q2)
BRAND NEW DATA!
Very Preliminary
Proton MAID Model
RED RSS. (Hall C, NH3,ND3)
BLUE E01-012. (Hall A, 3He)
Neutron
GREEN E97-110. (Hall A, 3He)
stat only
49
d2(Q2)
E08-027 g2p
SANE
6 GeV Experiments Sane just completed in Hall
C g2p in Hall A, 2011
projected
d2n just completed in Hall A
50
Planned d2n with JLab 12 GeV
  • Projections with 12 GeV experiments
  • Improved Lattice Calculation (QCDSF,
    hep-lat/0506017)

51
Color Polarizabilities
52
f2 Extraction and Color Polarizabilities
  • JLab world n data,
  • m4 (0.019-0.024)M2
  • Twist-4 term
  • m4 (a24d24f2)M2/9
  • extracted from m4 term f2
    0.034-0.005-0.043
  • f2 can be measured from g3
  • Color polarizabilities
  • cE 0.033-0.029
  • cB -0.001-0.016
  • Proton and p-n
  • f2 -0.160-0.179 (p),
  • -0.136-0.109 (p-n)

PLB 93 (2004) 212001
53
Transverse Spin (II) Single Spin Asymmetries in
SIDIS
Transversity and TMDs
54
Transversity
  • Three twist-2 quark distributions
  • Momentum distributions q(x,Q2) q?(x) q?(x)
  • Longitudinal spin distributions ?q(x,Q2) q?(x)
    - q?(x)
  • Transversity distributions dq(x,Q2) q-(x) -
    q-(x)
  • It takes two chiral-odd objects to measure
    transversity
  • Semi-inclusive DIS
  • Chiral-odd distributions function (transversity)
  • Chiral-odd fragmentation function (Collins
    function)
  • TMDs (without integrating over PT)
  • Distribution functions depends on x, k- and Q2
    dq, f1T- (x,k- ,Q2),
  • Fragmentation functions depends on z, p- and Q2
    D, H1(x,p- ,Q2)
  • Measured asymmetries depends on x, z, P- and Q2
    Collins, Sivers,
  • (k-, p- and P- are related)

55
Leading-Twist TMD Quark Distributions
Nucleon
Unpol.
Trans.
Long.
Quark
Unpol.
Long.
Trans.
56
Current Status
  • Large single spin asymmetry in pp-gtpX
  • Collins Asymmetries
  • - sizable for proton (HERMES and COMPASS)
  • large at high x, p- and p has
    opposite sign
  • unfavored Collins fragmentation as large
    as favored (opposite sign)?
  • - consistent with 0 for deuteron (COMPASS)
  • Sivers Asymmetries
  • - non-zero for p from proton (HERMES),
    consistent with zero (COMPASS)?
  • - consistent with zero for p- from proton and
    for all channels from deuteron
  • - large for K ?
  • Very active theoretical and experimental study
  • RHIC-spin, JLab (Hall A 6 GeV, CLAS12,
    HallA/C 12 GeV), Belle, FAIR (PAX)
  • Global Fits/models by Anselmino et al., Yuan et
    al. and
  • First neutron measurement from Hall A 6 GeV
    (E06-010)

57
E06-010 Single Target-Spin Asymmetry in
Semi-Inclusive n?(e,e'p/-) Reaction on a
Transversely Polarized 3He Target
First neutron measurement 7 PhD
Students Completed data taking in Feb. Exceeded
PAC approved goal
Collins
Sivers
58
Hall-A Transversity
en?epX
en?eKX
Polarized 3He effective polarized neutron
target World highest polarized luminosity
1036 New record in polarization gt70 without
beam 65 in beam and with spin-flip (proposal
42)
HRSL for hadrons (p- and K-), new RICH
commissioned BigBite for electrons, 64 msr,
detectors performing well
59
Target Performance
  • Online preliminary EPR/NMR analysis shows a
    stable 65 polarization with 15 mA beam and 20
    minute spin flip

Online Preliminary
60
Projections of g1T
  • First Neutron (3He) Measurement
  • With Fast Beam Helicity Flip (30Hz)
  • Projected Uncertainties (Stat. Only)
  • 2.3 at low x
  • 3.4 at high x

61
Precision Study of Transversity and TMDs
  • From exploration to precision study
  • Transversity fundamental PDFs, tensor charge
  • TMDs provide 3-d structure information of the
    nucleon
  • Learn about quark orbital angular momentum
  • Multi-dimensional mapping of TMDs
  • 3-d (x,z,P- )
  • Q2 dependence
  • Multi-facilities, global effort
  • Precision ? high statistics
  • high luminosity and large acceptance

62
Add new hall
12
6 GeV CEBAF
11
63
12 GeV Upgrade Kinematical Reach
  • Reach a broad DIS region
  • Precision SIDIS for transversity and TMDs
  • Experimental study/test of factorization
  • Decisive inclusive DIS measurements at high-x
  • Study GPDs

64
Solenoid detector for SIDIS at 11 GeV
Proposed for PVDIS at 11 GeV

GEMs
65
3-D Mapping of Collins/Siver Asymmetries at JLab
12 GeV With A Large Acceptance Solenoid Detector
  • Both p and p-
  • For one z bin
  • (0.5-0.6)
  • Will obtain 4
  • z bins (0.3-0.7)
  • Upgraded PID for K and K-

66
3-D Projections for Collins and Sivers Asymmetry
(p)
67
Discussion
  • Unprecedented precision 3-d mapping of SSA
  • Collins and Sivers
  • p, p- and K, K-
  • Study factorization with x and z-dependences
  • Study PT dependence
  • Combining with CLAS12 proton and world data
  • extract transversity and fragmentation functions
    for both u and d quarks
  • determine tensor charge
  • study TMDs for both valence and sea quarks
  • study quark orbital angular momentum
  • Combining with world data, especially data from
    high energy facilities
  • study Q2 evolution
  • Global efforts (experimentalists and theorists),
    global analysis
  • much better understanding of 3-d nucleon
    structure and QCD

68
Spin Structure with the Solenoid at JLab 12 GeV
  • Program on neutron spin structure with polarized
    3He and solenoid
  • Polarized 3He target
  • effective polarized neutron
  • highest polarized luminosity 1036
  • A solenoid with detector package (GEM, EM
    calorimeter Cherenkov
  • large acceptance 700 msr for
    polarized (without baffles)
  • ? high luminosity and large acceptance
  • Inclusive DIS improve by a factor of 10-100
  • A1 at high-x high precision
  • d2 at high Q2 very high precision
  • parity violating spin structure g3/g5
    first significant measurement
  • SIDIS improve by a factor of 100-1000
  • transversity and TMDs,
  • spin-flavor decomposition (2 orders
    improvement)
  • Unpolarized luminosity 5x1038 , acceptance
    300 msr (with baffles)
  • Parity-Violating DIS
  • Boer-Mulders function

69
Single Spin Asymmetries in (Qausi-)Ealstic
Two-photon Exchange and GPDs
70
E05-015 Target Single Spin Asymmetry Ay
  • Inclusive quasi-elastic electron scattering on
    vertically polarized 3He target
  • Target Single Spin Asymmetry Ay0 in one-photon
    approximation, two-photon exchange gives non-zero
    Ay.
  • Elastic contribution is well-known,
  • inelastic response provides a new way to access
    the Generalized Parton Distributions.

71
E05-015 Projection
  • Neutron data provide unique new constraints on
    GPDs.
  • Measurements at Q20.5, 1.0 GeV2
  • (and 2 GeV2).
  • GPD model prediction and expected uncertainty
    (2x10-3) at Q21.0 GeV2.
  • Data taken competed two weeks ago,
  • exceeded approved goal.
  • First clear non-zero asymmetry measurement _at_ 10s
    level
  • ? Established quantitatively the
  • 2-photon-exchange mechanism.
  • ? Established it as a tool to precisely
  • probe hadron structure.

Blue curve elastic contrib. Black curve
inelastic contrib. Red point total contrib.
72
Summary
  • Spin structure study full of surprises and
    puzzles
  • A decade of experiments from JLab exciting
    results
  • valence spin structure, quark-hadron duality
  • spin sum rules and polarizabilities
  • test cPT calculations, ? dLT puzzle
  • precision measurements of g2/d2 high-twist
  • first neutron transversity measurement
  • first quasi-elastic target SSA 2-photon to
    probe GPDs
  • JLab played a major role in recent experimental
    efforts
  • shed light on our understanding of STRONG QCD
  • lead to breakthrough?
  • Bright future
  • complete a chapter in spin structure study with 6
    GeV JLab
  • 12 GeV Upgrade will greatly enhance our
    capability
  • Goal a full understanding of nucleon structure
    and strong interaction
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